Starting circuit for high intensity short arc lamps



May 16, 1967 N. c. BEESE 3,320,476

STARTING CIRCUIT FOR HIGH INTENSITY SHORT ARC LAMPS Filed Aug. 21, 1964 65 VOLTS D.C. C5 I I I20 vou's 5 60 A.C. SOURCE Fig; Y

M P Q s I20 VOLTS 5y i 60 my INVENTOR NORMAN C. BEESE ATTORNEY United States Patent 3,320,476 STARTING CIRCUIT FOR HIGH INTENSITY SHORT ARC LAMPS Norman C. Beese, Verona, N.J., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Aug. 21, 1964, Ser. No. 391,346 Claims. (Cl. 315-289) The present invention relates to electrical discharge lamps and more particularly to high intensity short are lamps which operate at high temperatures and pressures.

As is well known in the art, short are lamps consist generally of an anode and a cathode located within a sealed quartz envelope containing an inert gas such as xenon, mercury, krypton, etc., which is maintained under high pressure of the order of about 20 atmospheres. The anode and cathode are axially aligned within the envelope and relatively positioned with their tip ends spaced a short distance from each other for producing an intense are having a very useful continuous spectrum adapting the lamp to a variety of uses.

High intensity short arc lamps have not been used heretofore to an extent corresponding to their efficiency since their use has been limited by some disadvantages. Difficulties have been encountered in starting the lamps since this requires high voltages and often results in damaging the quartz envelope and lamp housing. Such lamps require voltage of the order of 25 kv. to 50 kv., for starting and especially for reigniting, when the lamps are in heated condition. These high voltages also produce objection able radio interference. The starting voltages can and have been reduced by assembling a third or starting electrode in the lamp, however, it has been observed than an appreciable amount of power and elapsed time is required in order to develop the required intense gas ionization at the cathode and the diffusion of the ions to the anode for igniting the are between the cathode and anode.

The present invention is directed to a high intensity short arc lamp having a third or auxiliary electrode located in closely spaced relation with the cathode and to circuitry for starting the lamp.

One object of the invention is to provide circuitry which improves the reliability of starting high intensity short arc lamps utilizing an auxiliary electrode.

Another object is to provide starting circuitry for highintensity short-arc lamps which require a minimum of auxiliary equipment.

Another object is to provide circuitry which reduces substantially the voltages required for starting a high intensity short-arc lamp.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a schematic presentation of the starting circuitry for the lamp which is diagrammatically shown.

FIGURE 2 is a view similar to FIGURE 1 but showing a modification of a portion of the circuitry of FIG- URE 1.

In FIGURE 1, the lamp is represented at L and has the usual anode indicated at A and cathode indicated at B. Additionally, an auxiliary or starting electrode indicated at E is provided and as shown is positioned in the vicinity of the cathode B. The most desirable position for the starting electrode E is about 2 mm. above the cathode and about 2 mm. off the arc axis between anode A and cathode B as generally shown in the figure. This location of electrode E will assist the convection gas currents during the initial ignition cycle in sweeping the ionized gas into the space between the cathode and anode and form a conducting path for the main arc stream.

By using the electrode arrangement shown in the drawings and the circuitry therefor, which will be described, the starting voltage can be reduced substantially from that required for a two electrode lamp of generally similar geometrical and physical constructions.

The starting circuit is operated from an AC. source, for example, a 60 cycle or 400 cycle, volt power supply. The power supply is connected to a transformer T which is operative to step up the voltage to between 3 and 7 kilowatts. The secondary of transformer T is connected to a condenser C through a current limiting resistor R and the condenser C is in turn connected to the primary of a second transformer T and to a spark gap 10. The inductance of the primary winding of transformer T the condenser C and the spark gap 10 combine to produce a high frequency oscillatory or pulsing circuit of several megacycles resonant frequency. This high frequency voltage is transmitted through the secondary of transformer T to a pulse network, the starting electrode E of the lamp L and a voltage divider by line 15. The transformer T is of the step-up air core type having an output voltage of 10 to 15 kilovolts which is supplied to the three lamp electrodes through condenser C resistor R and line X when switch S is closed.

Arc ignition can be accelerated if a positive bias, of the order of 500 to 2000 volts, is applied to the anode A while 5000 to 10,000 volts are applied between cathode B and starting electrode E. Application of the voltage in this manner will extract ions and electrons from the plasma in the arc zone, and increase the gas ionization during preignition more effectively than normal D.C. line voltage which is used to operate the lamp. The voltage divider circuit is indicated generally at 20, consists of resistors R and R and condenser C and C, as shown in FIGURE 1 and provides one means of applying the desired voltage, for example, of between 500 and 2000 volts to the anode A by line 16 while applying 5 to 10 kilovolts between the starting electrode E and cathode B by lines 15 and Y. The voltage is supplied to anode A during the time the high frequency pulses are supplied by the oscillatory circuit to the starting electrode E by line X when switch S is closed. The particular voltage divider 20 in FIGURE 1 has the relationship of R C equals R times C and provides a device whereby the same voltage phase exists between the starting electrode E and the anode A. The ratio of resistors 4 ad- 4 determines the division of the voltage between the anode A and the starting electrode E.

The modification of FIGURE 2 is similar in all respects to the circuit of FIGURE 1 with the exception of the pulse network which is indicated at 25 and differs from network 20 by replacing the condenser C of FIGURE 1 with a rectifier V in FIGURE 2 to eliminate the AC. components of the high frequency pulses and applying the desired voltage to the anode.

The lamp L may be operated conveniently from a D.C. source, for example, of 6-5 volts indicated in the drawings and to start the lamp, switches S S S S and S are closed in this sequence and after the arc is established between electrodes A and B by the starting circuitry above described, the switches S S S and S will be Opened and the lamp will be operated from the D.C. source. Power from the 65 volt D.C. supply flows through an ammeter indicated at M, variable current control resistance P and a choke coil Q, which is provided to minimize voltage ripples in the power supply and then through lines X and Y, since switch S is 3 closed, to the anode A and to cathode B. A condenser C is provided to confine the high frequency oscillations to the starting circuit when the switch S is closed.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A high intensity short-arc discharge lamp formed of a light transmissive discharge vessel containing an ionizable atmosphere and having an anode and a cathode electrode spaced from each other to support an arc path therebetween in combination with starting circuitry for initiating discharge between the anode and cathode comprising,

(a) an auxiliary electrode within the discharge vessel and positioned adjacent said cathode,

(b) an alternating current source and transformer means for stepping up voltage from said source,

(c) said transformer means having means for producing high frequency voltage oscillations,

(d) first circuitry connecting the auxiliary electrode and the cathode with the transformer means for applying the high frequency voltage between the auxiliary electrode and cathode,

(e) second circuitry connecting the anode and the cathode with the transformer means for applying the high frequency voltage between the anode and the cathode,

(f) said first circuitry having voltage divider means therein,

(g) said voltage divider means having a connection to the anode for applying a selected portion of the voltage to the anode and (h) a direct current source connected across the anode and cathode.

2. A high intensity short arc lamp as set forth in claim 1 and having the starting circuitry of claim 1, further characterized by the auxiliary electrode of paragraph (a) located between the anode and cathode and off the arc axis.

3. A high intensity short are lamp as set forth in claim 1 and having the starting circuitry of claim 1, further characterized by the transformer means of paragraph (b) including an air core transformer having a spark gap, a capacitor and a resistor in its primary circuit for producing the high frequency voltage oscillations of paragraph (c).

4. A high intensity short are lamp as in claim 1 and having the starting circuitry of claim 1, further characterized by the transformer means of paragraph (b) being operative to step up the voltage to between 10,000

and 15,000 volts and to produce voltage oscillationsof several megacycles resonant frequency and the voltage 5 applied by the first circuitry of paragraph (d) is between 5,000 and 10,000 volts while the voltage applied by the second circuitry of paragraph (c) is between 500 and 2,000 volts.

5. A high intensity short-arc discharge lamp formed of a light transmissive discharge vessel containing an ionizable atmosphere and having an anode and a cathode electrode spaced from each other to support an arc path therebetween in combination with starting circuitry for initiating discharge between the anode and cathode comprising,

(a) an auxiliary electrode within the discharge vessel and positioned adjacent said cathode,

(b) an alternating current source and transformer means for stepping up voltage from said source,

(c) said transformer means having means for producing high frequency voltage oscillations,

(d) first circuitry connecting the auxiliary electrode and the cathode with the transformer means for applying the high frequency voltage between the auxiliary electrode and cathode,

(e) second circuitry connecting the anode and the cathode with the transformer means for applying the high frequency voltage between the anode and the cathode,

(f) said first circuitry having voltage divider means therein,

(g) said voltage divider means having a connection to the anode for applying a selected portion of the voltage to the anode,

(h) switch means in the first and second circuitries for cutting Off the alternating current supp-1y and (i) a direct current source across the anode and the cathode for maintaining the arc path after the alternating current supply is cut off.

References Cited by the Examiner UNITED STATES PATENTS 7/ 1956 Germeshausen 315-289 6/1965 Nuckolls 3l5174 12/1965 Clark 315-175 

1. A HIGH INTENSITY SHORT-ARC DISCHARGE LAMP FORMED OF A LIGHT TRANSMISSIVE DISCHARGE VESSEL CONTAINING AN IONIZABLE ATMOSPHERE AND HAVING AN ANODE AND A CATHODE ELECTRODE SPACED FROM EACH OTHER TO SUPPORT AN ARC PATH THEREBETWEEN IN COMBINATION WITH STARTING CIRCUITRY FOR INITIATING DISCHARGE BETWEEN THE ANODE AND CATHODE COMPRISING, (A) AN AUXILIARY ELECTRODE WITHIN THE DISCHARGE VESSEL AND POSITIONED ADJACENT SAID CATHODE, (B) AN ALTERNATING CURRENT SOURCE AND TRANSFORMER MEANS FOR STEPPING UP VOLTAGE FROM SAID SOURCE, (C) SAID TRANSFORMER MEANS HAVING MEANS FOR PRODUCING HIGH FREQUENCY VOLTAGE OSCILLATIONS, (D) FIRST CIRCUITRY CONNECTING THE AUXILIARY ELECTRODE AND THE CATHODE WITH THE TRANSFORMER MEANS FOR APPLYING THE HIGH FREQUENCY VOLTAGE BETWEEN THE AUXILIARY ELECTRODE AND CATHODE, (E) SECOND CIRCUITRY CONNECTING THE ANODE AND THE CATHODE WITH THE TRANSFORMER MEANS FOR APPLYING THE HIGH FREQUENCY VOLTAGE BETWEEN THE ANODE AND THE CATHODE, (F) SAID FIRST CIRCUITRY HAVING VOLTAGE DIVIDER MEANS THEREIN, (G) SAID VOLTAGE DIVIDER MEANS HAVING A CONNECTION TO THE ANODE FOR APPLYING A SELECTED PORTION OF THE VOLTAGE TO THE ANODE AND (H) A DIRECT CURRENT SOURCE CONNECTED ACROSS THE ANODE AND CATHODE. 